1. Field of the Invention
The present invention relates to systems for controlling the cooling of components in an enclosed environment, such as those in a micro- or mini-computer system. More specifically, the invention relates to the use of cooling baffles and arrangement of various system components to enhance the cooling of certain heat-sensitive internal components.
2. Description of Related Technology
Many electrically powered systems include environments having heat-producing elements contained within a substantially enclosed area. For example, within a typical computer system, the heat generated internally by certain components such as integrated circuit devices, power supplies, motors and transformers, may be substantial. Such heat must be dissipated at a rate sufficient to maintain the temperature of critical system components at an acceptable level in order to preclude premature component and system failure. While small increases in operating temperature may not be immediately detrimental to the operation of such components, long term operation at these elevated temperature levels may adversely impact their longevity and reliability. This is particularly true of comparatively sensitive integrated circuit or data storage devices such as the central processing unit (CPU) or disk drives, respectively, which may suffer disproportional reductions in longevity with incremental increases in operating temperature. Additionally, mechanical effects resulting from wide variations in temperature and high peak temperatures may eventually induce component failures.
It has been recognized that temperature-sensitive components such as ICs and disk drives often act as significant heat sources themselves. In such cases, it may not be sufficient to simply maintain the ambient air within the computer chassis at a temperature below the maximum allowable temperature for these devices, since each device may not dissipate heat effectively enough to maintain its temperature within acceptable limits. Localized or forced cooling of these components often must be used to increase the rate of heat transfer.
Generally, increased cooling of computer components may be accomplished by enhanced convective, radiant or conductive heat transfer out of the component. Heat sinks are sometimes used to enhance conductive heat transfer by conducting heat from the component into the sink, which is then cooled by convective (and to a much lesser degree, radiative) heat transfer. Assuming air as the cooling medium and a constant inlet temperature, convective cooling of a component, whether it has a heat sink or not, can be facilitated by increasing the airflow over the component and, depending upon the component and system configuration, inducing more laminar or more turbulent flow around the component.
Increased airflow can be obtained by increasing fan capacity, or alternatively, by reducing the obstructions to airflow around the components of concern. Hence, for a given fan capacity, simply relocating the heat-producing components with respect to existing air flow and making the flow path less tortuous can significantly enhance heat transfer. This is particularly true when these components are placed in direct proximity to the inlet of the cooling air, which has the lowest temperature of any region within the housing.
With respect to turbulence, inwardly blowing fans induce substantial turbulence in the chassis, especially in the vicinity of the fan discharge. Turbulent flow is generally more useful for removing heat from large surface-area components such as finnned heat sinks, while laminar flow is often preferable for other components. Discharge or exhaust systems create a more laminar flow within the chassis than do inlet systems, since the turbulence produced by the fan discharge is outside the chassis. Therefore, since most internal computer components are not equipped with heat sinks which can benefit from turbulence, laminar or linear flow is generally preferable.
In addition to the factors discussed above, dedicating the airflow created by a fan/inlet combination to a limited number of components can even further increase the cooling of those components. For example, providing a power supply with its own fan and source of inlet air is obviously more effective in terms of cooling than simply disposing the power supply within the interior of the computer (along with all of the other components) somewhere between the fan and the air inlet.
Taking the aforementioned concepts together, it can be seen that the cooling of internal computer components may generally be optimized through the use of a plurality of dedicated cooling fans placed in an exhaust orientation, and the location of critical components in direct proximity to dedicated air inlets.
A substantial number of cooling system configurations aimed at enhancing the cooling of heat producing components within the computer chassis are described in the prior art. These systems utilize a variety of different combinations of fan placement, internal component/board arrangement, ventilation hole placement, and electrical cable routing. For example, the prior art system of FIGS. 1 and 2 introduces air into the housing 120 via air inlets 10 and an inlet ventilation fan 20 located in the top, sides, or front of the chassis, and exhausts comparatively hotter air via one or more cooling fans 30 located at the rear of the chassis.
The placement of the critical components within these prior art systems, including the CPU 40, floppy disk drive cage 50, power supply 60, hard disk drive cage 70, and CD-ROM drive 80, is not optimized in that the components are only indirectly cooled by the inlet air, and/or some of the cooling air is diverted to components which do not require cooling. Furthermore, as shown in FIGS. 1 and 2, prior art computer systems do not coordinate the placement of heat-producing components with that of the fan and the air inlets such that substantially linear airflow is maintained throughout the interior volume of the computer; many systems create a tortuous airflow path 90 thereby effectively reducing the flow of air for a given fan capacity.
Other attempts at improving the air cooling of electrical components within an enclosed environment are disclosed in several United States patents, which are discussed below.
U.S Pat. No. 5,218,514 discloses a personal computer housing system having a plurality of air intakes located around the sides and front of the housing, with a fan mounted at the rear which draws air through the intakes. System I/O and expansion cards are mounted longitudinally from front to back at various orientations and elevations such that air drawn in the front and side intakes passes over the cards before being exhausted by the cooling fan. However, this arrangement provides a somewhat tortuous airflow path, thereby increasing flow resistance. Furthermore, air may circulate within substantially all of the interior volume of the enclosure, potentially cooling components which do not require cooling.
U.S Pat. No. 5,440,450 discloses a housing having an integrated cooling channel running linearly through one dimension of the computer chassis. A fan is mounted at one end of the channel, and heat radiating fins run the length of the channel. The heat producing power supply is mounted directly in contact with the channel. The motherboard is mounted adjacent to the channel such that some of the air being drawn into the intake of the channel by the cooling fan is ultimately passed over the motherboard (and CPU) before changing direction and being ingested into the channel. This air is drawn into the chassis through a series of perforations in the rear of the chassis. Hence, this arrangement suffers disabilities as those previously described in that the cooling airflow path is tortuous, and system efficiency is reduced through the cooling of non-critical components.
U.S. Pat. No. 5,432,674 discloses a computer tower unit having an internal airflow control baffle. The unit has two cooling fans (one "system" fan and one dedicated to the power supply unit) which draw air through a pair of exterior openings generally opposed from the fans. This arrangement obviates the need for a separate (i.e., third) disk drive cooling fan since the baffle redirects a portion of the air drawn in by the upper fan through the upper inlet to pass over the disk drive unit Air drawn in through the lower and upper inlets passes in part over the motherboard and CPU after being redirected. The baffle pivots outward during maintenance to permit access to the motherboard. In this system, the primary function of the baffle is redirection of the internal airflow of the unit (especially that originating from the lower inlet), which changes directions in several parts of the housing.
In view of the foregoing, it can be appreciated that existing enclosure cooling systems have not adequately solved the problems of optimizing the operating temperature of certain heat-sensitive components while maintaining high cooling system efficiency and minimizing electrical power requirements. Therefore, it would be most desirable to provide an improved cooling apparatus for a computer system which would overcome the limitations of the prior art and provide for the optimized cooling of critical system components while maintaining a high overall efficiency. Furthermore, it would be desirable to design such an apparatus to facilitate both the routing of internal system wiring and periodic system maintenance.